Method of manufacturing cylindrical self-induction coils comprising a ceramic core as a carrier for the winding



June 6, 1956 s. GALLEE 2,751,666

METHOD OF MANUFACTURING CYLINDRICAL SELF-INDUCTION COILS OMPRISING A CERAMIC CORE WINDING FJ' led No AS A CARRIER FOR THE v. 10 1951 Fig. 3

Fig. 2

Invenfop:

Stanis/aus @al/ee' y Aflo/ney United States Patent METHOD OF MANUFACTURING CYLINDRICAL SELF-INDUCTION C0115 CONIPRISING A CE- RAMIC CORE AS A CARRIER FOR THE WIND- ING Stanislaus Galle, Berlin-Zehlendorf, Germany, assignor to International Standard Electric Corporation, New

York, N. Y., a corporation of Delaware Application November 10, 1951, Serial No. 255,856

Claims priority, application Germany November 17, 1950 3 Claims. (Cl. 29-15558) This invention relates to the manufacture of cylindrical or approximately cylindrical self-induction coils and particularly to coils having a core made of a ceramic material.

With coils which are wound and have a protective glazing which is generally efiected at 400 or 500 degrees centigrade, the turns become loose on the core because the coeflicient of expansion of the materal of the turns is higher than that of the core. The turns may thus be caused to leave their correct position, and under certain circumstances shorts may occur. Thus the selfinduction values of equivalent coils may be quite different from each other. This can be counteracted to some extent by the provision of grooves in the core. As a rule, however, the latter defect can not be overcome in this way.

An object of this invention is to eliminate the drawbacks inherent in the above mentioned coils. To this end the invention, in order to manufacture cylindrical or approximately cylindrical self-induction coils, employs a ceramic hollow body which is slotted longitudinally or composed of several parts, and serves as a core to carry the coil. This ceramic body may have grooves, as has been the case heretofore, or may be without grooves. On such body the winding is arranged in the usual manner. In addition, however, a mandrel is inserted in the hollow body. The diameter of this mandrel corresponds to the internal diameter of the hollow body. The temperature coefficient of the mandrel is greater than, or at least equal to, the temperature COCfiIlClBHlZ of the material of the winding. The body or core, containing the mandrel and provided with the winding, is subjected to the usual heat treatment, in order to undergo the glazing process, as, for instance, in a muffie furnace containing an atmosphere of some protective gas.

An example of such process is as follows:

The mandrel, and the hollow body together with the winding are expanded by the heat. Since, however, the temperature coefiicient of the mandrel is greater than that of the winding, and the hollow body being either slotted or made in several parts, the winding will invariably be kept stretched, whereby its turns are safely prevented from getting loose and becoming entangled. As soon as the insulating coating has been heated to its melting point and thus undergoes the sintering operation, the winding is covered by the glazing so formed. This glazing, however, also enters the slots or separating joints of the hollow body and when the temperature is reduced for cooling, the glazing becomes solid. Since such solidification also occurs in the said slots or joints, the hollow body keeps the expanded condition despite the effect of cooling and thus continues to stretch the winding. A possible minor contraction of the hollow body need not be taken into account. In any case this body can not contract more than the winding on it. Although the resultant coil is somewhat larger in diameter than it was originally, the turns are held in the correct position so that they can not get loose or become entangled during the glazing process. It is also possible for that part of the glazing which is seated on the winding, to be removed afterwards, as for example, by grinding, whereby a self-induction coil will be obtained whose inductivity is variable, with the aid of a slider or the like, in the manner of the customary induction variometers and slider coils. The mandrel, which in cooling reassumes itsoriginal diameter, is easy to remove.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 shows one embodiment of the invention;

Fig. 2 shows a second embodiment of the invention in one stage of the inventive process;

Fig. 3 shows another stage of the embodiment of Fig.

Fig. 4 shows mandrel which may be used with the invention.

In Fig. l, 1 denotes a tubular body made of a ceramic material whose temperature coeflicient may be assumed to be 6x10 This body carries a winding 2 of copper wire whose temperature coefiicient is at 20Xl0- Inserted in body 1 and in close contact therewith is a cylindrical mandrel 4 made of aluminium and whose temperature coeflicient is 3O l0- Body 1 has a longitudinal slot 3.

While this embodiment of the invention is primarily suitable where body 1 is thin-walled, the constructions represented in Figs. 2 and 3 are also suitable if its walls are thicker. In Figs. 2 and 3 this body, likewise designated 1, is shown as made in three parts, 1', 1", 1'. The separating joints between theseare denoted by 3, 3", 3". Within body 1 the mandrel 4 is arranged, which is shown apart in Fig. 4. The winding is denoted by 2.

Figs. 1 and 2 relate to the initial state and Fig. 3 to the final state after mandrel 4 has been removed. Mandrel 4 is over its entire cylindrical surface in close contact with the interior surface of body 1. In order to be provided with a glazing the body 1, having the winding 2 coiled around it, is fitted with the respective coating and then placed into the furnace. As soon as the melting temperature has been reached the coating sinters and fills up the joints in body 1, which have been enlarged by the action of mandrel 4, by the heating, the temperature coeflicient of mandrel 4 being greater than the others and thus have caused the winding to be stretched as described. When the glazing on the winding and in the joints of body 1 is then permitted to cool down, it becomes solid. The solid glazing in the joints prevents body 1 from contracting so as to impair the stretched condition of the winding. Mandrel 4, which if desired may be made in several parts, is easy to remove from body 1 after the structure 1, 2, 4 has cooled down. In this way the coil illustrated in Fig. 3 results in a coil whose circumferential surface is enlarged by the width of the filled-up joints of body 1 and which is, therefore, somewhat larger in diameter than it was before.

As stated, the glazing on the winding may be removed afterwards. Instead of a slotted or two-part body 1 a body made in several parts may be employed. It is also possible for body 1 to be of non-cylindrical shape, provided that mandrel 4 be given a form which agrees with such other shape, so that also in this case the winding shall be stretched uniformly as described.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is only by way of example and not as a limitation to the scope of my g a 2,761,666 Q a invention as set. forth in .thenhjects thereof and in the accompanying claims.

What is claimed is:

1. The process of manufacturing an electrical coil mounted on a hollow core consisting of separable parts, comprising coating the winding and core with an insulatingmaterial, heating the winding and core thereby causing the winding, to expand and the insulator material to melt, separating the core by increasing the diameter thereof, thus increasing the tautness of. the wire and permitting the insulator material to enter the space therebetween, and solidifying the insulator to maintain the core in its enlarged form. V

2. The process according to claim 1 wherein the step of separating the core comprises inserting in the .core a mandrel having a temperature coeflicient at least equal to that of the winding, so that upon heating, the mandrel will expand with the winding thus separating the core by increasing the diameter thereof, and maintaining thewire taut, and said solidifying step comprises cooling the insua lating materal; said process further comprising the step of removing said mandrel from the core after said core is cooled. V

3. The process according to claim 2, wherein said mandrel and winding are heated at a temperature of approximately 400 C.

References Cited in the file of this patent UNITED STATES PAPENTS Freidrich July 13, 1926 

1. THE PROCESS OF MANUFACTURING AN ELECTRICAL COIL MOUNTED ON A HOLLOW CORE CONSISTING OF SEPARABLE PARTS, COMPRISING COATING THE WINDING AND CORE WITH AN INSULATING MATERIAL, HEATING THE WINDING AND CORE THEREBY CAUSING THE WINDING TO EXPAND AND THE INSULATOR MATERIAL TO MELT, SEPARATING THE CORE BY INCREASING THE DIAMETER THEREOF, THUS INCREASING THE TAUTNESS OF THE WIRE AND PERMITTING THE INSULATOR MATERIAL TO ENTER THE SPACE THEREBETWEEN, AND SOLIDIFYING THE INSULATOR TO MAINTAIN THE CORE IN ITS ENLARGED FORM. 